Fuel filter assembly with heater

ABSTRACT

A fuel filter assembly for diesel fuel includes a filter head structure, spin-on replaceable element and threaded collection bowl. An annular heater housing is secured in the filter head for warming the fuel prior to passage through the filter medium with a pair of positive temperature coefficient heater discs providing the self-regulating heater function. A check valve is housed in the inlet chamber of the filter head in bypass connection with the filter medium to vent air from the chamber and to establish a return path for fuel from the filter. A restrictive orifice in the check valve limits fuel flow in the bypass path and an elastomeric duck-bill type valve provides the check valve function.

This is a continuation of Ser. No. 242,791 filed on Sept. 9, 1988, nowabandoned which is a continuation of Ser. No. 032,834 filed on Mar. 30,1987, now abandoned which is a continuation-in-part of Ser. No. 784,292filed on Oct. 7, 1985, now U.S. Pat. No. 4,692,245, which is acontinuation-in-part of Ser. No. 733,808 filed on May 14, 1985, now U.S.Pat. No. 4,668,393.

BACKGROUND OF THE INVENTION

This invention relates to diesel fuel filters and more particularly to afuel filter which includes heater means therein for elevating thetemperature of the fuel to prevent buildup of residues and subsequentclogging of the fuel system.

The application of heater devices to diesel fuel filters has becomeaccepted in the field because of the successful results obtained and thefact that much wider temperature ranges can be accommodated, which hadpreviously introduced problems of clogging and plugging of the filters.While initially heaters were adapted to preexisting filter devices, ithas now become commonplace to incorporate the heater as an integral partof the filter assembly and to achieve an efficient heat transfer withthe fuel being passed to the filter element.

In particular, heater elements have been applied to the spin-on type offuel filter wherein it is desired not only to obtain an efficient heattransfer relationship, but also to provide an efficient housingstructure which can be incorporated safely into an engine compartmentand still provide relatively free access for filter changes, maintenanceand the like. Particular attention has been paid in such devices to theretention of a quantity of fuel in the filter head and/or the heaterelement so that when the filter element is exchanged there is not anexcessive spillage of fuel. An alternate scheme is to provide means forefficiently draining the filter casing or cartridge prior to removal ofthe spin-on element so as to avoid or minimize the fuel spillageproblem.

One device of this type is shown in U.S. Pat. No. 4,387,691 wherein aparticular form of heater structure is employed in the filter head of afilter assembly which includes a spin-on type of filter element.Particular attention is paid in this disclosure to the routing of fluidsthrough the heater structure and the filter medium so as to achieve anefficient and advantageous heat transfer relationship.

A similar arrangement of diesel fuel heater is shown in U.S. Pat. No.4,406,785 wherein a plurality of PTC fuel heater elements are disposedon a conductive plate and located within the filter head of a fuelfilter assembly to achieve the heat transfer relationship. In this formof apparatus, a circuitous path of travel for fluid flow through theheater element is provided which is on the order of 360° in angularlength and the heater is directly operative in the fuel path.

Still another form of prior art device is shown in U.S. Pat. No.4,596,224 wherein a separate insulative housing is provided for the fuelheater which housing is disposed between the filter head and the spin-onelement and in which, again, a circuitous path of travel for the fluidflow is provided.

A more recent disclosure is made in U.S. Pat. No. 4,608,161 wherein afuel heater structure is disposed in the filter head of the filterassembly. In this disclosure special structure is provided between thefilter head and the spin-on filter element to displace fuel which mighthave been trapped in this location and which avoids significant fuelspillage upon element replacement.

SUMMARY OF THE INVENTION

The apparatus of the instant invention is an improvement over thesetypes of devices in providing a heater structure which is located in thefilter head of a filter assembly, which filter assembly includes acompound spin-on element comprising a casing for a filter elementsubassembly together with a removable threaded collection bowl. Thisform of structure is particularly suited for the spin-on type of filterelement in providing a convenient and safe mechanism for accommodatingthe element exchange and also providing an efficient heat transferrelationship between the fuel heater and the diesel fuel passing throughthe filter apparatus.

The apparatus of the instant invention is particularly concerned with aspin-on diesel fuel filter structure which incorporates a number offeatures in the die cast head structure for the assembly. These include,among others, the heater element and a particular form of return checkvalve in fluid communication with an inlet chamber in the filter headfor releasing trapped air and for returning fuel to the fuel system ofthe engine. The die cast head assembly includes not only inlet andoutlet ports for interconnection with the fuel system of the vehicle,but also additional ports for the provision of a vent/calibration valveand a vacuum switch, both of which are in fluid communication with anoutlet chamber in the filter head.

The entire filter assembly is supported by the filter head which may beattached at any convenient location in the engine compartment.Interconnection with the replacement spin-on element is made by means ofa threaded tube in the filter head which provides not only the mountingdevice but also a means for securing the fuel heater in the filter headand making electrical connection therewith. The fuel heater is anannular can structure having a central mounting aperture adapted toreceive the threaded tube and consisting of an upper insulating housingand a lower conductive plate which is in electrical connection with thethreaded tube. A feed-through electrical contact and thermostat assemblyprovides electrical power to a pair of PTC-type heater elements disposedon the conductive plate. A circuitous fuel path is established so that asuitable heat transfer relationship is achieved with the heaterelements.

The spin-on element comprises a removable collection bowl which isthreadedly attached to an adaptor member secured in the spin-on elementcasing. The casing in turn is supported by a rigid top plate from thethreaded tube and contains therewithin the filter element subassemblycomprising an annular filter medium contained within upper and lower endcaps and surrounding a central perforated supported tube. A filter drainassembly and water sensor probe are included in the collection bowl forremoval of water and other contaminants or for removal of fluidpreparatory to exchange of the spin-on element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the fuel filter assembly of theinvention in a typical fuel supply and return system for a diesel engineand the like;

FIG. 2 is a plan view of the fuel filter assembly of the invention;

FIG. 3 is an elevational view of the fuel filter assembly of theinvention;

FIG. 4 is a sectional view of the fuel filter assembly of the invention;

FIG. 5 is a sectional view of the filter head portion of the fuel filterassembly;

FIG. 6 is a bottom view of the filter head assembly of FIG. 5; and

FIG. 7 is a sectional view of the return check valve used in the fuelfilter assembly.

DETAILED DESCRIPTION OF THE INVENTION

A fuel filter assembly 10 for filtering and heating fuel for dieselengines and the like comprises a filter head 12, a spin-on element 13and collection bowl 15. The filter head is fastened to an engine orother suitable structure by flange 16 and supports the entire fuelfilter assembly 10. Preferably, filter head 12 is a die cast head andincludes therein typical inlet port 18, outlet port 19, and connectedrespectively thereto, inlet chamber 21 and outlet chamber 22. Filterhead 12 is a generally circular structure having a flat annular mountingsurface 24 at the lower portion thereof for sealing engagement by thespin-on element 13 and further includes annular cavity 25 forming a partof inlet chamber 21 and surrounding a circular portion of outlet chamber22. Heater assembly 26 is received in cavity 25 of inlet chamber 21 andis secured in place by threaded tube 28, the central portion of whichcommunicates with outlet chamber 22. Filter head 12 further comprisesvent port 29 and vacuum switch port 30, both of which are in fluidcommunication with outlet chamber 22 and return check valve port 31which is in fluid communication with inlet chamber 21. Still further,filter head 12 includes the heater port 32 which houses a feed throughconnector 34 and thermostat 35 for supplying electrical power to heaterassembly 26.

Referring to FIG. 1, the fuel supply system for a typical diesel engineis depicted in schematic form as comprising fuel tank 40, fuel pump 41,the fuel filter assembly 10 of the instant invention, injection pump 42and a plurality of injectors 44. Typical fuel lines are interconnectedamong the various components of the system with, for example, fuel line45 connected to the inlet port 18 of filter assembly 10 and with variousbleed lines 46 providing a fuel return path from each of the injectors44 to the fuel tank 40. Bleed line 47 is also depicted as returning fuelfrom injection pump 42 to fuel tank 40 as a part of the fuel system. Notdepicted in FIG. 1 but understood as comprising a part of the fuelsystem, are pressure lines between the injection pump 42 and each of theinjectors 44 which supply fuel to the diesel engine. A further bleedline 48 is shown as connected between fuel filter assembly 10 and fueltank 40 by way of bleed lines such as 46, this being the line which isconnected from a return check valve 50 connected at the return checkvalve port 31. In turn, port 31 is connected to inlet chamber 21 offilter head 12 for venting air and fuel from fuel filter assembly 10which air is entrained in the diesel fuel or which is trapped thereinupon change of the spin-on element 13.

Referring now more particularly to the cross sectional view of FIG. 4,spin-on element 13 is seen to comprise cylindrical casing 52 whichhouses filter element 54 for separating out contaminants and particulatematter in the fuel passing through the filter assembly. Filter element54 comprises filter medium 55 which is an annulus or loop of pleatedpaper element well known in the art or any other form of filter mediumwhich would be suitable for separating out contaminants. Filter medium55 is housed between upper end cap 56 and lower end cap 57 each of whichcomprise generally circular sheet metal plates for supporting the filterstructure. Both of the end caps 56, 57 include circular ridges at theouter periphery thereof which extend inwardly of the filter medium 55 tofurther contain the structure. A perforated central support tube 58 ishoused in the center of the structure centrally of the filter medium 55and all of the elements are secured together by means of pottingcompound closely adjacent the inner surfaces of the upper and bottom endcaps 56, 57 respectively. Therefore it is apparent that filter medium 55divides the spin-on element casing 52 into an outer peripheral fuelchamber 60 and a central fuel chamber 61.

Filter element 54 further includes rigid top plate 62 which is generallyof circular configuration having a central threaded aperture 64 and aplurality of openings 65 which surround the central aperture and providea path for fuel flow through the top plate 62. An annular gasket 66 isprovided above top plate 62 and which is retained in place on thespin-on element 13 to provide sealed engagement with mounting surface 24of filter head 12. Spin on element 13 further comprises an inner annulargasket 68 which is pressed in place on a central opening in upper endcap 56 and retained in position by being trapped between end cap 56 andtop plate 62. Gasket 68 provides a seal for spin-on element 13 when inengagement with a smooth portion of the outer periphery of threaded tube28 as depicted in FIG. 4. At the lower portion thereof, spin-on element13 further comprises adaptor ring 69 which is a continuous rinq adaptedto lie flat and be sealed against a lower turned-in edge of casing 52 bymeans of a polyester adhesive material. Adaptor ring 69 includes aplurality of radially oriented and circumferentially distributedupstanding ribs 70 and a depending annular threaded portion 71 forsecurement of collection bowl 15. Upstanding ribs 70 provide fluid paths72 therebetween for flow of contaminants and the like to the interior ofcollection bowl 15.

Spin-on element 13 is fabricated by placement and adhesion of adaptorring 69 against the lower turned-in end of casing 52. Thereafter, filterelement 54, as a subassembly, is positioned on the ribs 70 of adaptorring 69 thereby forming the fluid paths 72. Inner annular gasket 68 isplaced in position in the central opening of upper end cap 56 and topplate 62 placed thereover with the material forming the central threadedaperture 64 pressed into an inner peripheral opening of gasket 68. Athin metal plate covering top plate 62 and welded in place thereto isthen secured to casing 52 by means of a rolled edge to secure the entirespin-on element assembly 13. Annular gasket 66 is positioned in anannular groove above top plate 62 and is retained in place therein byseveral indented portions. A more detailed description of spin-onelement 13 may be obtained in co-pending application Ser. No. 784,292,assigned to the assignee of the instant invention, which is incorporatedherein by reference.

Referring now to the collection bowl 15 shown at the lower portion ofspin-on element 13 in FIG. 4, this device comprises a cup-like memberhaving bottom wall 73 and peripheral side wall 74. The latter has aninternally threaded portion thereon and culminates at the upper edge inan annular groove in which o-ring seal 76 is disposed for sealingengagement with the lower surface of the turned-in edge of casing 52.Collection bowl 15 has a filter drain assembly 78 mounted in the lowerportion thereof for disposing of water accumulated in the collectionbowl and for draining of the entire spin-on element 13 upon replacementof the latter. Filter drain 78 comprises pop-up valve 79 mounted in anopening in bottom wall 73 of collection bowl 15 as well as vent valve 80which is adapted to allow air to be drawn into the collection bowl 15 torelieve the partial vacuum created therein on opening of pop-up valve79. Further mounted in lower wall 73 of collection bowl 15 is a watersensor probe 82 which is an insulated electrical conductor adapted toachieve electrical continuity with fluid in the collection bowl when thefluid rises to a level to contact its exposed inner end.

Heater assembly 26 is shown in more detail in the views of FIGS. 5 and 6as comprising an annular container formed essentially of an upperinsulating cover 84 and a lower conductive cup 85 which are joined attheir margins and staked in place to provide a fuel heater enclosure 86of generally annular configuration. Upper insulated cover 84 isdepressed at the central portion thereof to form the inner margin ofannular enclosure 86 and is received on a central stud in filter head 12for securement in inlet chamber 21. Lower conductive cup 85 is depressedat two locations about its lower wall, spaced 180° apart for receipt ofa pair of heater element discs 88 which are the devices which supply thethermal energy for warming of the diesel fuel passing through heaterassembly 26. Heater discs 88 are positive temperature coefficient (PTC)semiconductor elements which are commonly employed for similar purposesand which have a self-regulating thermal capability due to theirrelatively high positive temperature coefficient. This providesregulation of the electrical input and thus, the power output of theheater discs. A conductive plate of generally half-ring configuration isjoined to the inner end of feed through connector 34 and thermostat 35to supply electrical power to one side of heater discs 88 by means of aplurality of spring fingers 90 depending from conductive plate 89 at thelocation of each of discs 88. As noted, lower conductive cup 85 is incontact with threaded tube 28 which in turn is threaded into filter head12, and with all of these devices made of highly conductive metal, thisarrangement provides an efficient ground connection for the heaterassembly 26.

Feed through connector 44 and thermostat 35 are combined as asubassembly for insertion in an opening in upper insulated cover 84, thelatter being sealed by means of an o-ring engagement with filter head 12while the thermostat 35 itself is sealed on the interior with a furthero-ring. As noted more clearly in the view of FIG. 6, heater assembly 26includes an outlet aperture 92 in the lower conductive cup 85, an inletaperture 94 in the upper insulated cover 84 and a barrier consisting ofradially positioned wall 95 extending downwardly from upper cover 84 tothe lower conductive cup 85 to provide a blockage in the annular fuelenclosure 86 in heater assembly 26. Thus, fuel entering inlet port 18and inlet chamber 21 of filter head 12 is directed to the upper cover 84of heater assembly 26 and into inlet opening 94, to be passed in acircuitous path of approximately 360° over and around the heaterelements discs 88 to outlet opening 92 in lower conductive cup 85. Fuelthen flows to the space between filter head 12 and top plate 62 ofspin-on element 13 to pass through the openings 65 in the top plate andinto outer peripheral fuel chamber 60. As fuel traverses filter medium55 moisture and other contaminants are collected on the outer surfacethereof and drop to the bottom of casing 52, thereafter to pass throughthe fluid paths 72 in adaptor ring 69 and to be collected in collectionbowl 15. Fuel that traverses filter medium 55 enters perforated tube 58and the central fuel chamber 61 and is delivered through threaded tube28 to outlet chamber 22 and outlet port 19 for delivery to a furtherpart of the fuel system of the vehicle.

In replacement of the spin-on element 13 it is only necessary to actuatethe filter drain 79 and remove not only contaminants from collectionbowl 15 but also fuel that may be entrained in filter medium 55,peripheral fuel chamber 60 and the cavities located above the spin-onelement 13. Element 13 may then be unthreaded from filter head 12 andremoved therefrom for replacement purposes. During this procedure,collection bowl 15 is unthreaded from spin-on element 13, a new spin-onelement introduced to which the collection bowl 15 is threaded andsecured in position and the entire new spin-on element 13 attached tothreaded tube 28 to be secured to filter head 12. At this point a vacuumcould be applied to vent valve 96 which is merely a check valve threadedinto vent valve port 29 to draw fuel throughout the filter assemblyuntil the outlet chamber 22 is filled or alternatively a fuel supplypump as at 41 could be actuated to force fluid through the filterassembly until the apparatus is again filled. In this procedure air thathas been introduced into the assembly during interchange of spin-onelement 13 will tend to rise to the top of inlet chamber 21 and air thatis entrained in the diesel fuel will similarly rise to the top of inletchamber 21. At this location return check valve 50 will become operativeto vent air from the chamber and fluid as well to the return line 48 tobe returned eventually to the fuel tank 40. In this manner aconsiderable amount of air which had previously been trapped in the fuelfilter assembly will be expunged therefrom to provide more reliableoperating characteristics.

Referring to the FIG. 7 cross sectional view, return check valve 50comprises metal body member 101 having a hex portion thereon, anexternally threaded inner end, and a central axial stepped bore 103therein. The outer end portion of body 101 is a reduced tubular parthaving barbs 104 thereon and a closure member 105 at the outer end toprovide a fitting for push on tubing or the like to serve as a drainline for return of fuel to a fuel tank 40. Closure member 105 includes asmall central orifice 106 therein which is typically on the order of0.040 inches in diameter and which serves as a device to restrict flowof fuel through the return check valve 50. Inner end 107 of bore 103 isenlarged and the bore 103 is stepped in several locations toward theoutlet end at orifice 106. Seated in bore 103, against shoulder 108 ischeck valve 110 which is a single piece elastomeric part in the form ofa duck-bill valve. Check valve 110 comprises a circular entrance ring114 of relatively thick proportions, a tubular portion 115 and a pair oflips 116 in the shape of a duck's bill which provides a check valvefunction for the valve 110. The lips 116 taper inwardly from tubularportion 115 and are closely adjacent one another at their downstream endto provide a seal against fluid flow in the reverse direction, but aresufficiently flexible to be distended slightly upon fluid flow from theinlet of check valve 50 toward the orifice 106 to provide very littleresistance to such fluid flow. Similarly, air that is trapped withininlet chamber 21 of filter head 12, passes with the fluid through checkvalve 50 to fuel tank 40. The relatively small size of outlet orifice106 in return check valve 50 assures that while a substantiallycontinuous flow of fluid is provided such flow will be restricted to arelatively minimal amount sufficient to assure clearance of entrappedair in filter head 12. Since return check valve 50 is connected frominlet chamber 21 to the fuel tank 40 it will be noted that it is inbypass connection of filter medium 55 and does provide some relief forexcessive pressure differentials exhibited at the filter medium 55. Itwill be noted that the vacuum switch 98 of conventional variety isthreaded in vacuum switch port 30 of filter head 12 in fluidcommunication with outlet port 19 so as to provide an indication of thepressure level in this chamber and a signal of the clogging orcontamination of filter medium 55 so that replacement can be performedas necessary.

We claim:
 1. A fuel filter assembly for filtering and heating dieselfuel and the like, comprisinga filter head for supporting the filterassembly and for interconnection with the fuel system of an engine,inlet and outlet ports in said filter head in fluid communicationrespectively with inlet and outlet chambers in said filter head, anannular fuel heater in said inlet chamber for receiving and circulatingfuel during heating thereof, said fuel heater having plural positivetemperature coefficient heater elements therein, and adapted to receivediesel fuel from said inlet port and heat the fuel in said inletchamber, a threaded tube in fluid communication with said outletchamber, said threaded tube supporting said fuel heater in tightphysical and electrical engagement with said filter head, a third portin said filter head having an electrical feed through connector thereinin electrical connection with said fuel heater for supplying electricalpower thereto, a filter casing receiving on said threaded tube insealing engagement with said threaded tube and with said filter head, afilter medium extending in a loop within said casing and separating acentral fuel chamber from a peripheral fuel chamber, said central fuelchamber and said peripheral fuel chamber being in fluid communicationrespectively with said outlet chamber and with said inlet chamber insaid filter head, said filter casing being replaceable on said threadedtube, an air vent outlet port in said filter head for externalconnection to the fuel system of the engine, and return check valvemeans in said filter head in fluid communication with said inlet chamberfor releasing trapped air and for returning fuel through said air ventoutlet port to the fuel system of the engine.
 2. The fuel filter ofclaim 1 further comprising a collection bowl removably attached to saidcasing, said casing having a fluid path for flow of contaminant betweensaid peripheral fuel chamber and said collection bowl.
 3. The fuelfilter of claim 2 further comprising threaded connector means supportedin said casing for engagement by said collection bowl whereby saidcollection bowl may be threadedly detached from said casing.
 4. The fuelfilter of claim 3 wherein said casing comprises a cylindrical casingsupporting a rigid circular top plate having fuel entry holes thereinand a central threaded aperture for interconnection with said threadedtube, an outer annular seal above said top plate for sealing againstsaid filter head and an inner annular seal below said top plate forsealing against said threaded tube, both of said seals being replaceablewith said casing.
 5. The fuel filter of claim 4 wherein said casingsupports said filter medium therein by means of impervious upper andlower circular end caps in close engagement with the upper and lowerends of said filter medium, and a central perforated tube extendingbetween said upper and lower end caps.
 6. The fuel filter of claim 5further comprising potting compound on the inner surfaces of said upperend cap and said lower end cap for sealingly securing said centralperforated tube, said filter medium and said upper and lower end caps asan integral filter element.
 7. A fuel filter for filtering and heatingdiesel fuel and the like, comprisinga spin-on cylindrical element, afilter head assembly having an annular mounting surface thereon forsealingly receiving said spin-on cylindrical element, inlet and outletports in said filter head in fluid communication respectively with inletand outlet chambers in said filter head, a fuel heater in said inletchamber for warming fuel prior to passage to said spin-on element, afilter element in said spin-on element for separating out contaminantsin the diesel fuel and for establishing a flow path for diesel fuelbetween an outer peripheral fuel chamber and a central fuel chamber,said peripheral fuel chamber being in direct fluid communication withsaid inlet chamber in said filter head and said central fuel chamberbeing in direct communication with said outlet fuel chamber in saidfilter head, means for releasably interconnecting said spin-on elementand said filter head, and valve means in said filter head forestablishing a path for fluid to flow to the exterior of said filterhead from said inlet chamber for venting of air and fuel from said inletchamber at a location upstream of said filter element.
 8. The fuelfilter of claim 7 wherein said valve means comprises a check valveadapted for interconnection with the fuel system of an engine forreturning diesel fuel from said inlet chamber to said fuel system. 9.The fuel filter of claim 7 wherein said valve means comprises a checkvalve and restricted orifice means for limiting the flow of fuel throughsaid check valve in bypass of said filter element.
 10. The fuel filterof claim 9 wherein said means releasably interconnecting said spin-onelement and said filter head is a threaded tube secured in said filterhead, said threaded tube securing said fuel heater in electricalengagement with said filter head.
 11. The fuel filter of claim 10wherein said threaded tube is in fluid communication with said outletchamber in said filter head, establishing a path for fluid flow fromsaid spin-on element to said outlet chamber.
 12. The fuel filter ofclaim 11 wherein said filter head further comprises a vent port and avacuum switch port in fluid communication with said outlet chamber insaid filter head, said vent port having therein a vent valve for ventingand filling said outlet chamber, and said vacuum switch port providingaccess to said outlet chamber for monitoring the vacuum pressure in saidoutlet chamber.
 13. The fuel filter of claim 9 wherein said check valveis an elastomeric duck-bill check valve supported in a body memberthreaded into a port communicating with said inlet chamber.
 14. The fuelfilter of claim 7 wherein said spin-on cylindrical element has anannular mounting surface, and including means for releasablyinterconnecting a contaminant collection bowl and said spin-on elementwith said contaminant collection bowl sealing engaging said annularmounting surface of said spin-on element.
 15. A fuel filter assembly forfiltering and heating diesel fuel and the like, comprising:a filter headfor supporting the filter assembly and for interconnection with the fuelsystem of an engine, said filter head including inlet and outletchambers, inlet and outlet ports in said filter head in fluidcommunication with said inlet and outlet chambers, respectively, a fuelheater in said inlet chamber for heating fuel in said inlet chamber, afilter casing, means for securing said filter casing to said filterhead, a filter medium within said casing and separating a central fuelchamber from a peripheral fuel chamber, said central fuel chamber andsaid peripheral fuel chamber being in fluid communication respectivelywith said outlet chamber and with said inlet chamber in said filterhead, an air vent outlet port in said filter head for externalconnection to the fuel system of the engine, and return check valvemeans in said filter head in fluid communication with said inlet chamberfor releasing trapped air and for returning fuel through said air ventoutlet port to the fuel system of the engine.
 16. The fuel filter ofclaim 15 including a threaded tube in fluid communication with saidoutlet chamber, and wherein said filter casing is removably received onsaid threaded tube in sealing engagement with said threaded tube andwith said filter head.
 17. The fuel filter of claim 16 wherein saidthreaded tube supports said fuel heater in tight physical and electricalengagement with said filter head, said fuel heater includes an annulararrangement of plural positive temperature coefficient heater elements,and said filter head includes a third port having an electrical feedthrough connector therein in electrical connection with said fuel heaterfor supplying electrical power to said fuel heater.
 18. The fuel filterof claim 15 wherein said return check valve means is an elastomericduck-bill check valve.
 19. The fuel filter of claim 18 wherein saidelastomeric duck-bill check valve is supported in a body member threadedinto said air vent outlet port.
 20. The fuel filter of claim 15 furthercomprising a collection bowl removably attached to said casing, saidcasing having a fluid path for flow of contaminants between saidperipheral fuel chamber and said collection bowl.